In a conference call with reporters, senior Obama administration officials speaking on background said the resettlement program, dating to the post-Vietnam war era, provides "the most rigorous screening" for any travelers to the United States.

Refugees looking to resettle here face a phalanx of federal agencies directly or indirectly checking the applicants' backgrounds, they said. The rules apply to all refugees coming to the U.S. under the program, including the 10,000 Syrian refugees Obama has pledged to bring here in light of the current crisis.

The entry process has multiple steps, they said:

Individuals are referred, often through the United Nations' refugee program. The UN, however, does not do the background checks on applicants.

Applicants are interviewed by trained screeners for biographical details. Their stories are checked against records if they exist or if not, intelligence collected by the federal government.

Applicants are fingerprinted if their records are not already available, and those records are checked against intelligence gathered by the FBI and Homeland Security.

The government consults with nine non-profits that work with community organizations and churches to find homes and, if possible, low-level jobs for able-bodied adults.

The interviews of Syrian applicants are done by trained State Department staffers in Amman, Jordan; Istanbul, Turkey; and Cairo, they said. The administration officials said their agencies are looking for employees to volunteer to assist in screening applicants.

The administration is trying to make the process, one official said, "more efficient without cutting corners on security."

In all the process takes from 18 months to 24 months, a senior administration official said.

Many refugee applicants lack personal documentation, but not so in past experience with many Syrians, a senior Homeland Security official said.

"Syrians tend to be a very, very heavily documented population," the official said.

Syrian applicants over the years have fared about as well as refugee applicants from other countries, the officials said, with about roughly half approved and the other half either denied or put in pending status.

Before the current refugee crisis began this past summer, about 50 percent of the Syrian refugee applicants were children, 25 percent were adults over age 60 and about 2 percent were single males of "combat age," an official said.

While the program is run by the federal bureaucracy, it depends on Congress to keep it funded and communities to embrace the refugees.

A senior State Department official acknowledged demands by more than two dozen governors, including Christie, to not resettle Syrian refugees in their states.

However, states can only consult on the process, the official said, noting that once they are permitted to resettle, refugees have rights under the Constitution.

The administration officials said they are reaching out to members of congress and governors to explain the process to them.

The conference call was offered in part to blunt growing numbers of legislators and governors calling for a halt to resettling refugees from the Middle East following the terrorist attacks last week in Paris.

Meanwhile, a Rutgers-Eagleton poll earlier this year found a rising percentage of New Jersey residents believing the state housed too many immigrants, and the recent events in Paris likely will increase that number.

"Especially given last week's attacks and the rhetoric that has emerged from 2016 candidates, New Jerseyans might be much less accepting of refugees now, compared to both immigrants from other countries, as well as compared to even a few weeks ago prior to the attacks," said Ashley Koning, assistant director of the Eagleton Center for Public Interest Polling.